JPH11140610A - Production of aluminum alloy structural material excellent in toughness and weldability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a material excellent in toughness and weldability by casting an Al alloy in which the contents of Zn, Cu, Mg, Ti, Cr, Zr, rare earth elements or the like are specified and the content of Si is prescribed and controlling the conditions in hot rolling. SOLUTION: An Al alloy having a compsn. contg., by weight, 5.0 to 8.0% Zn, 2.0 to 3.0% Cu, 1.2 to 2.8% Mg, 0.005 to 0.3% Ti, 0.05 to 0.3% Cr, 0.05 to 0.15% Zr, <=0.03% Mn, 0.01 to 0.2% V, 0.05 to 0.15% misch metal, 0.01 to 0.25% Fe, and the balance Al, and in which the content of Si is regulated to <=0.1% is cast. This Al ingot is subjected to hot rolling composed of initial hot rolling 1 in which the rolling starting temp. is regulated to 380 to 450 deg.C, the finishing temp. to 350 to 400 deg.C, and the thickness to from 0.95 to 0.9 T, intermediate hot rolling 1 in which the thickness is regulated to from 0.5 to 0.33 T, intermediate hot rolling 2 in which the thickness is regulated to from 2.0 to 1.3 (t) and final rolling in which the thickness is regulated to 1.0 (t). The drafts and rolling rates in the intermediate hot rolling 1 and 2 are respectively regulated to 10 to 15 mm/pass, 40 to 70 m/min, 20 to 40 mm/pass and 70 to 130 m/min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a high-strength aluminum alloy structural material having excellent toughness and weldability.

[0002]

2. Description of the Related Art Age-hardening type Al-Zn-Mg-Cu based 7075 alloy, 7175
Alloy, 7N01 alloy such as Al-Zn-Mg alloy
000 series alloy is used. Especially Al-Zn-Mg
-Cu-based alloys are used for aircraft because of their high strength and excellent toughness and specific strength. By the way, toughness is the most important characteristic in terms of reliability in structural materials. For example, in the case of the 7000 series alloy, when aging treatment (T6 treatment) is performed to the maximum strength, fracture toughness is reduced.
The overaging treatment (T73 treatment) imparts toughness even at the expense of strength.

[0003] The cause of the decrease in toughness of the 7000 series alloys is the Al-Cu-Mg system, Al-F crystallized during solidification.
An intermetallic compound such as an e-Si system, an Al-Fe system, or an Al-Fe-Cu system remains in a product without being partially dissolved. For this reason, 7050-T736 treated material or 71, which regulates the amount of impurities such as Fe and Si that impair toughness.
75-T736 treatment materials and the like have been developed. Further, a method in which hot rolling is performed twice and the crystallized material is re-dissolved (first rolling at 300 to 480 ° C. → 4 at 450 to 525 ° C.)
Time uniform heat treatment → second rolling at 300 to 420 ° C)
(Japanese Patent Publication No. 63-60820).

[0004] On the other hand, aluminum alloys are considered to be difficult to weld compared to steel materials because aluminum alloys have good thermal conductivity, a large coefficient of thermal expansion, and an oxide film is easily formed on the surface. Advances in welding equipment, welding construction methods, and the like have led to the use of aluminum alloy welded structures in railway vehicles, ships, chemical and food industry equipment, and aerospace equipment. However, 7000
Since the system alloy is a heat-treated alloy, cracks are formed in the welded portions, and strength (particularly, proof stress) of the welded portions is reduced. Therefore, mechanical joining mainly by bolts and rivets is used for joining of the 7000 series alloy, and welding is limited to special applications. In addition, among 7000 series alloys, 7N0
Alloy 1 is excellent in roll formability, weldability, stress corrosion cracking resistance, etc., but has the disadvantage of poor mechanical strength. in this way,
Conventionally, there has been no high-strength aluminum alloy structural material excellent in toughness and weldability.

[0005]

In view of such circumstances, the present inventors have focused on crystallized substances that impair the toughness, studied their refinement by refining and re-solidifying, and studied the improvement of Ti and rare earth elements. We researched the improvement of weldability by adding Cu and processing conditions. As a result, a method for producing a high-strength aluminum alloy structural material excellent in toughness and weldability, which cannot be obtained with the conventional 7000 series alloy, has been developed.

[0006]

According to the present invention, Zn is added to 5.0.
~ 8.0 wt%, Cu 2.0 ~ 3.0 wt%, Mg 1.
2 to 2.8 wt%, 0.005 to 0.3 wt% Ti, Cr
0.05-0.3wt%, Zr 0.05-0.15wt
%, Mn is 0.03 wt% or less, and V is 0.01 to 0.2 wt%.
%, MM (Misch metal) 0.05 ~ 0.15wt
%, 0.01 to 0.25 wt% of Fe, and 0.1% of Si.
A method for producing a structural material in which an aluminum alloy substantially consisting of Al is melted and cast, and the obtained ingot is subjected to hot rolling, cold rolling, and finish rolling in this order. A rolling start temperature of 380 to 450 ° C,
Rolling end temperature is 350-400 ° C., and rolling from ingot thickness T to rolled material thickness 0.95T-0.9T is initial rolling,
Rolling to a rolled material thickness of 0.5T to 0.33T after the initial rolling is performed by intermediate hot rolling 1 and intermediate hot rolling 1 and a rolled material thickness of 2.0.
When the rolling from t (t is the hot rolling end thickness) to 1.3 t is the intermediate hot rolling 2, and the rolling to the rolling material thickness 1.0t after the intermediate hot rolling 2 is the final rolling, Hot rolling 1 is performed with a rolling reduction of 10 to 15 mm / pass and a rolling speed of 40 to 70 m / pass.
And the intermediate hot rolling 2 is performed under the conditions of
This is a method for producing an aluminum alloy structural material excellent in toughness and weldability, characterized by being applied under the conditions of 0 mm / pass and a rolling speed of 70 to 130 m / min.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The alloying elements according to the present invention will be described below. Zn is an element indispensable for improving the strength. The reason for defining the content to be 5.0 to 8.0 wt% is that if the content is less than 5.0 wt%, the effect cannot be sufficiently obtained.
If the content exceeds 8.0 wt%, toughness, weldability, and stress corrosion cracking resistance are reduced. Cu is an element indispensable for strength improvement like Zn. The content is 2.0-
The reason why the content is specified as 3.0 wt% is that if the content is less than 2.0 wt%, the effect cannot be sufficiently obtained, and if the content exceeds 3.0 wt%, toughness and weldability are reduced. Mg is an element indispensable for strength improvement like Zn. Its content is 1.2-2.
The reason for defining the content to be 8 wt% is that if the content is less than 1.2 wt%, the effect cannot be sufficiently obtained, and if the content exceeds 2.8 wt%, the toughness is reduced.

[0008] Ti refines the structure and improves the weldability. The reason that the content is defined as 0.005 to 0.3 wt% is that if the content is less than 0.005 wt%, the effect cannot be sufficiently obtained, and if it exceeds 0.3 wt%, the giant compound crystallized at the time of casting remains. This is because the toughness of the product decreases. Cr refines the crystal structure and improves weldability. The reason for defining the content to be 0.05 to 0.3% by weight is that the content is 0.1%.
If the content is less than 05 wt%, the effect cannot be sufficiently obtained.
%, The giant compound crystallized at the time of casting remains to lower the toughness of the product. Zr refines the crystal structure and improves the weldability. The content is 0.05 to 0.1.
The reason for specifying 15 wt% is that if the content is less than 0.05 wt%, the effect cannot be sufficiently obtained, and if it exceeds 0.15 wt%, a giant compound crystallized at the time of casting remains and the toughness of the product decreases. is there.

Mn contributes to stabilization of the crystal structure. The reason for defining the content to be 0.03% by weight or less is as follows.
If the content exceeds wt%, a giant compound crystallized at the time of casting remains and the toughness of the product decreases. V also contributes to stabilization of the crystal structure similarly to Mn. The content is 0.01 to
The reason for specifying 0.2 wt% is that if it is less than 0.01 wt%, its effect cannot be sufficiently obtained, and if it exceeds 0.2 wt%, the giant compound crystallized at the time of casting remains and the toughness of the product decreases. It is. MM improves weld crack resistance. The reason for defining the content to be 0.05 to 0.15 wt% is as follows.
If the content is less than 5 wt%, the effect cannot be sufficiently obtained.
%, The giant compound crystallized at the time of casting remains to lower the toughness of the product. MM is La, Ce, N
a mixture of rare earth elements such as d, La, Ce, N
The same effect can be obtained by using d alone.

[0010] Fe contributes to improvement in strength. The reason for defining the content to be 0.01 to 0.25 wt% is that 0.01 wt%
%, The effect cannot be sufficiently obtained, and if it exceeds 0.25 wt%, a giant compound crystallized at the time of casting remains to reduce the toughness of the product, and the amount of solute Cu in the matrix decreases, resulting in aging. This is because the curing properties are reduced. The reason for specifying the Si content to be 0.1 wt% or less is that if the content exceeds 0.1 wt%, coarse Mg-Si-based compounds are generated during the soaking treatment, and the product strength is reduced.

Next, the manufacturing method of the present invention will be described.
The structural material of the present invention is melting, casting, hot rolling, cold rolling,
It is manufactured by a normal manufacturing process in which finish rolling is performed in order.
In the present invention, the starting temperature of hot rolling is set to 380 to 450.
When the temperature is lower than 380 ° C., internal cracking due to internal strain occurs, or as shown in FIGS. If the amount exceeds the above range, a crocodile mouth due to high-temperature embrittlement as seen in an Al-Mg alloy is generated. In FIG. 1, reference numeral 3 denotes a rolling roll. The reason for defining the end temperature of hot rolling at 350 to 400 ° C. is that if the temperature is lower than 350 ° C., internal cracking or alligator due to internal strain occurs, and if it exceeds 400 ° C., the internal and external portions of the rolled material due to processing heat This is because the temperature difference becomes large and a crocodile mouth is easily generated.

In the present invention, the reason why the rolling reduction in the intermediate hot rolling 1 is defined as 10 to 15 mm / pass is 10 mm.
If the number of passes is less than / pass, the calorific value of the working decreases and the internal strain increases, causing internal cracking or crocodile mouth.
This is because if the width exceeds 5 mm / pass, an alligator is generated due to a difference in temperature between the inside and the outside due to the heat generated during processing. The reason for setting the rolling speed in the intermediate hot rolling 1 to 40 to 70 m / min is as follows.
If it is less than 40 m / min, the temperature of the rolled material decreases, the deformation resistance increases, and cracks occur. If it exceeds 70 m / min, the temperature of the rolled material rises abnormally due to heat generated during processing.

In the present invention, the reason why the rolling reduction in the intermediate hot rolling 2 is defined as 20 to 40 mm / pass is as follows.
When the thickness is less than / pass, the middle part of the sheet thickness does not change sufficiently into a processed structure, and the crystal grain size of the middle part of the sheet thickness increases after T6 treatment, and the toughness decreases. This is because peeling occurs. In the present invention, the reason why the rolling speed in the intermediate hot rolling 2 is specified to be 70 to 130 m / min is that the surface area of the rolled material is widened in the intermediate hot rolling 2 and the temperature is easily lowered. This is because the temperature decreases, the deformation resistance increases, and the workability deteriorates. On the other hand, if it exceeds 130 m / min, the temperature of the rolled material due to the heat generated by processing increases abnormally.

According to the present invention, there is no need to perform hot rolling in two separate steps as in the prior art, and a structural material excellent in toughness and weldability can be obtained by continuous rolling, regardless of the sheet thickness, and productivity can be improved. Excellent. The present invention is used as a rolled material, an extruded material, and a forged material.

In the present invention, the rolling conditions for the initial rolling and the final rolling are not particularly set, but in the initial rolling, the ingot is usually easily rolled, so that the ingot is lightly reduced. Rolling may be performed under the same conditions as in rolling 1. In the final rolling, rolling may be performed under the same conditions as in the intermediate hot rolling 2.

[0016]

The present invention will be described below in detail with reference to examples. (Example 1) Alloys of the compositions of the present invention shown in Table 1 (Nos. A to H)
Was cast into a plate-shaped ingot having a thickness of 500 mm by a semi-continuous water-cooled casting method. Next, the ingot was subjected to a strain relief annealing at 350 to 400 ° C. for 2 hours and a homogenizing heat treatment at 470 ° C. for 5 hours, which was initially rolled to 450 mm, and then subjected to an intermediate heat treatment to a thickness of 200 mm. Cold rolling 1 then 10
Hot-rolled sheet 2 to 0 mm, and further subjected to final rolling to obtain a hot-rolled sheet having a thickness of 25 to 50 mm.
For 2 hours and aging treatment at 120 ° C. for 24 hours to obtain a plate-shaped structural material. The starting temperature and the ending temperature of the hot rolling, the rolling reduction and the rolling speed of the intermediate hot rolling 1 and the intermediate hot rolling 2 were variously changed.

(Comparative Example 1) Alloys of Comparative Example Compositions shown in Table 2
(No. I to N), and a plate-like structural material was produced in the same manner as in Example 1 except that rolling was performed under the conditions of the present invention.

Each of the obtained plate-like structural members was subjected to a toughness test and a weld crack resistance test by the following methods. The results are shown in Tables 3 and 4 together with the rolling conditions [Toughness test] (a) Test piece: 40 mm wide and 60 m long shown in FIG.
m, a tear test piece 1 having a thickness of 6 mm, an angle of 45 degrees and a depth of 10
A V-shaped notch 4 of mm was formed. V-shaped notch 4 bottom 5
Was formed to 0.025R. The bottom 5 of this V-shaped notch 4
And the center of the tensile force application point 6 were formed on a straight line. (B) Test method: Using an Amsler universal testing machine, the test piece was pulled by applying a chuck to the point of action 6 of tensile force, and A (the area of the hatched portion in FIG. 3) was determined from the obtained tensile load-displacement curve. , Which is substituted into the following equation to determine the tear resistance UP
E was sought. UPE = A / S (where S is the effective area of the test piece) (c) Evaluation method: The tear resistance value UPE was determined according to the following three criteria. Good (○): 2.0kg ・ mm / mm ² or more. Slightly poor (△): Less than 2.0 kg · mm / mm ² and 1.0 kg · mm / mm ² or more. Bad (×) ... 1.0kg · mm / mm less than ^2. [Weld Cracking Resistance Test] (a) Test piece: A fishbone type test piece in which the cutting depth was changed stepwise was used as the test piece after welding shown in FIG. In FIG. 4, L0 = 114 mm, L1 = 105 mm, L
2 = 12.7 mm, L3 = 1.2 mm, W0 = 66.8
mm, W1 = 55 mm, W2 = 9.6 mm. (B) Welding conditions: welding method: TIG, filler metal: not used, electrode rod: 3.2 mmφ cerium-containing W rod, welding current: 180 A, arc voltage: 19 V, welding speed: 30 m
m / min, argon gas flow rate ... 10 liter / mi
n. (C) Evaluation method: The crack length (Ic shown in FIG. 4) was determined according to the following three criteria. Good (O): Crack length less than 30 mm. Slightly poor (△): Crack length 30 mm or more and less than 50 mm. Poor (x): crack length 50 mm or more.

(Comparative Example 2) A plate-shaped structural material was manufactured in the same manner as in Example 1 except that rolling was performed under conditions outside the range specified in the present invention using the alloys of No. B shown in Table 1. , A toughness test and a welding resistance test were performed. Table 5 shows the results.

(Conventional Example 1) Using a conventional 7075 alloy,
A plate-like structural material was produced in the same manner as in Example 1 except that hot rolling was performed twice in accordance with the method disclosed in JP-B-63-60820, and a toughness test and welding resistance were performed. The test was performed. Table 6 shows the results.

[0021]

[Table 1] (Note) Nos. A to H are alloys of the present invention.

[0022]

[Table 2] (Note) Nos. I to N are comparative alloys.

[0023]

[Table 3] (Note) Intermediate hot rolling 1: 450 mm or less 200 mm or more. The rolling reduction is in mm per pass, and the rolling speed is in m / min. Intermediate hot rolling 2: less than 200mm 100mm or more. The amount of reduction and speed are the same. Tear resistance, unit: kg · mm / mm ² . Crack length, unit: mm.

[0024]

[Table 4] (Note)-are the same as (Note) in Table 3.

[0025]

[Table 5] (Note)-are the same as (Note) in Table 3. * Out of the specified value of the present invention.

[0026]

[Table 6] (Note) P7075 (Al-0.40Si-0.5Fe-1.5Cu-0.3Mn-2.5Mg-0.2Cr-5.5Zn-0.2Ti: wt%). Q7175 (Al-0.15Si-0.2Fe-1.5Cu-0.1Mn-2.5Mg-0.2Cr-6.8Zn-0.2Ti: wt%). Rolling start temperature, unit ° C. Rolling rate, unit%. Unit ℃. Unit hr. Same as (Note) in Table 3. Same as (Note) in Table 3.

As is clear from Table 3, No. 1 of the present invention example
No. 8 were excellent in toughness and weld crack resistance. On the other hand, in Nos. 9 to 14 of Comparative Example 1, since the alloy composition was out of the range specified in the present invention, as shown in Table 4, the toughness or weld cracking resistance was reduced. As shown in Table 5, the production conditions of Nos. 15 to 20 of Comparative Example 2 were out of the examples of the present invention, so that the toughness and weld crack resistance were reduced. No. 21 and 22 of the conventional example are shown in Table 6.
As shown in (2), the heat treatment was performed twice, but the toughness and weld cracking resistance were reduced because the crystallized material remained without re-dissolving sufficiently.

[0028]

As described above, according to the method of the present invention, a high-strength aluminum alloy structural material having excellent toughness and weldability can be efficiently produced by using a normal continuous rolling method and selecting the rolling conditions. It can be manufactured well and has an industrially significant effect.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view of the state of occurrence of crocodile mouths in hot rolling, (a) shows a state before rolling, (b) shows a state during rolling, and (c) shows a state after rolling.

FIG. 2 is an explanatory diagram of a test piece for a toughness test.

FIG. 3 is a diagram showing a tensile load-displacement curve in a toughness test.

FIG. 4 is an explanatory view of a fishbone type test piece for a weldability test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Alligator 2 Rolled material 3 Rolling roll 4 V-shaped notch 5 Bottom of V-shaped notch (0.025R) 6 Tensile force action point

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 683 C22F 1/00 683 685 685Z 694 694A 694B

Claims (1)

[Claims] 1. A Zn content of 5.0 to 8.0 wt% and a Cu content of 2.
0-3.0 wt%, Mg 1.2-2.8 wt%, Ti 0.005-0.3 wt%, Cr 0.05-0.3 wt%
%, Zr 0.05-0.15 wt%, Mn 0.03 wt%
%, V is 0.01 to 0.2 wt%, MM (Misch metal) is 0.05 to 0.15 wt%, and Fe is 0.01 to 0.2 wt%.
0.25 wt%, Si is regulated to 0.1 wt% or less,
In a method for producing a structural material in which an aluminum alloy substantially consisting of Al is melt-cast and the obtained ingot is subjected to hot rolling, cold rolling, and finish rolling, the hot rolling is performed at a rolling start temperature of 380 to 380. 450 ° C, rolling end temperature 350-4
00 ° C, rolled material thickness 0.95T ~
Rolling to 0.9T is the initial rolling, rolling after the initial rolling is 0.5T to 0.33T, the intermediate hot rolling is 1, the intermediate hot rolling is 1, and the rolling material thickness is 2.0t (t is When the rolling up to the hot rolling end thickness) to 1.3 t is defined as intermediate hot rolling 2 and the intermediate hot rolling 2 is followed by the rolling up to the rolling material thickness 1.0 t as the final rolling, the intermediate hot rolling 1 The rolling amount is 10 to 15 mm
And hot rolling at a rolling speed of 40 to 70 m / min, and applying the intermediate hot rolling 2 at a rolling reduction of 20 to 40 mm / pass at a rolling speed of 70 to 130 m / min. Method for manufacturing aluminum alloy structural materials with excellent performance.